package tw.idv.gasolin.pycontw2012.util;

import java.lang.reflect.Array;

//XXX these should be changed to reflect the actual memory allocator we use.
//it looks like right now objects want to be powers of 2 minus 8
//and the array size eats another 4 bytes

/**
 * ArrayUtils contains some methods that you can call to find out the most
 * efficient increments by which to grow arrays.
 */
public class ArrayUtils {

    private static Object[] EMPTY = new Object[0];
    private static final int CACHE_SIZE = 73;
    private static Object[] sCache = new Object[CACHE_SIZE];

    private ArrayUtils() { /* cannot be instantiated */
    }

    public static int idealByteArraySize(int need) {
        for ( int i = 4; i < 32; i++ )
            if ( need <= ( 1 << i ) - 12 )
                return ( 1 << i ) - 12;

        return need;
    }

    public static int idealBooleanArraySize(int need) {
        return idealByteArraySize(need);
    }

    public static int idealShortArraySize(int need) {
        return idealByteArraySize(need * 2) / 2;
    }

    public static int idealCharArraySize(int need) {
        return idealByteArraySize(need * 2) / 2;
    }

    public static int idealIntArraySize(int need) {
        return idealByteArraySize(need * 4) / 4;
    }

    public static int idealFloatArraySize(int need) {
        return idealByteArraySize(need * 4) / 4;
    }

    public static int idealObjectArraySize(int need) {
        return idealByteArraySize(need * 4) / 4;
    }

    public static int idealLongArraySize(int need) {
        return idealByteArraySize(need * 8) / 8;
    }

    /**
     * Checks if the beginnings of two byte arrays are equal.
     * 
     * @param array1
     *            the first byte array
     * @param array2
     *            the second byte array
     * @param length
     *            the number of bytes to check
     * @return true if they're equal, false otherwise
     */
    public static boolean equals(byte[] array1, byte[] array2, int length) {
        if ( array1 == array2 ) {
            return true;
        }
        if ( array1 == null || array2 == null || array1.length < length
            || array2.length < length ) {
            return false;
        }
        for ( int i = 0; i < length; i++ ) {
            if ( array1[i] != array2[i] ) {
                return false;
            }
        }
        return true;
    }

    /**
     * Returns an empty array of the specified type. The intent is that it will
     * return the same empty array every time to avoid reallocation, although
     * this is not guaranteed.
     */
    public static <T> T[] emptyArray(Class<T> kind) {
        if ( kind == Object.class ) {
            return (T[]) EMPTY;
        }

        int bucket = ( ( System.identityHashCode(kind) / 8 ) & 0x7FFFFFFF )
            % CACHE_SIZE;
        Object cache = sCache[bucket];

        if ( cache == null || cache.getClass()
            .getComponentType() != kind ) {
            cache = Array.newInstance(kind, 0);
            sCache[bucket] = cache;

            // Log.e("cache", "new empty " + kind.getName() + " at " + bucket);
        }

        return (T[]) cache;
    }

    /**
     * Checks that value is present as at least one of the elements of the
     * array.
     * 
     * @param array
     *            the array to check in
     * @param value
     *            the value to check for
     * @return true if the value is present in the array
     */
    public static <T> boolean contains(T[] array, T value) {
        for ( T element : array ) {
            if ( element == null ) {
                if ( value == null )
                    return true;
            } else {
                if ( value != null && element.equals(value) )
                    return true;
            }
        }
        return false;
    }
    
}
